A widely used interconnection system for electrical components comprises a relatively large circuit board, commonly referred to as a mother board, having a plurality of circuit board edge connectors mounted on one surface thereof. The circuit board edge connectors are adapted to receive the edge portions of smaller printed circuit boards, commonly referred to as daughter boards, and the connectors serve to connect terminal pads or conductors on the daughter boards to conductors on the mother board thereby to achieve the required circuits among the numerous components mounted on the daughter boards. Interconnection systems of this type are highly versatile and completely serviceable, since the daughter boards can be individually removed from their respective connectors and replaced for service purposes.
The increasing complexity of electrical and electronic equipment and the continuing reductions in the sizes of the electrical components used gives rise to the demand for circuit board connectors of smaller and smaller dimensions which are capable of accommodating daughter boards having their terminal pads on closer and closer center-to-center distances. Additionally, there are increasing requirements for circuit board edge connectors capable of receiving daughter boards having relatively large numbers of terminal pads thereon, for example, daughter boards with up to 200 terminal pads located along one edge are coming into widespread use, and the connectors for these daughter boards must be capable of receiving these edge portions and establishing contact with each of the terminal pads on the daughter board.
A further requirement of circuit board edge connectors is that the connector be designed such that an adequate contact force will be developed at each of the electrical interfaces between the contact terminals in the connector and the terminal pads on the daughter board. When the contact terminals and the terminal pads are gold plated, the contact force at each electrical interface need not be excessively high, but if a contact material other than gold is used on the circuit board, for reasons of economy, a relatively high contact force is required. For example, while 200 grams is commonly considered to be adequate for gold plated contacts, a force of 600 grams is required if the contact meterial is of tin or a tin-lead alloy.
The present invention is directed to the achievement of an improved circuit board edge connector which will satisfy the increasingly severe requirements of edge connectors which are now being specified by equipment manufacturers. The invention is thus directed to the achievement of a circuit board edge connector which has the capability of providing a relatively high contact force at each of the electrical interfaces established when a circuit board is mated with a connector, which provides contact terminals in the connector on closely spaced centers so that it can be used with circuit boards having terminal pads on like centers, and which can be produced with a relatively large number of contact terminals therein so that it is capable of accommodating circuit boards having a high number of terminal pads. The invention is further directed to the achievement of circuit board edge connector which is highly compact relative to its capacity to receive a circuit board of given dimensions and which can be mounted on a mother board in a stack of closely spaced connectors, thereby to achieve extremely high density of electrical connections within a limited space.
A preferred form of circuit board edge connector in accordance with the invention comprises a housing assembly which consists of an insulating housing, a metallic frame assembly on the housing, and a camming means mounted in the frame assembly. The frame assembly has one wall portion which is spaced from a board engaging surface of the insulating housing, thereby defining a trough into which edge portions of a circuit board are inserted. The camming means mounted on the frame assembly engages one surface of the circuit board after it has been inserted and pushes the circuit board against the board engaging surface of the housing, thereby to press the terminal pads on the circuit board against contact portions of the contact terminals which are contained in the insulating housing. The camming means is movable laterally with respect to the board engaging surface so that circuit boards of varying thicknesses can be accommodated by the connector. A spring means on the housing assembly urges the camming means towards the board engaging surface and provides a controlled and predetermined contact force at each of the electrical interfaces where the contact terminals bear against the terminal pads on the circuit board.